1. Field of the Invention
The present invention relates to a fastener used where an electric conductive plastic material (for example, CFRP (carbon fiber reinforced plastic)) is used as an outer skin of an aircraft, and, in particular, to a lightning protection fastener.
2. Description of the Related Art
As a fastener used when an electric conductive plastic material is used as an outer skin of an aircraft, a fastener disclosed in the Specification of U.S. Pat. No. 4,630,168 is known, in which one end surface of a head section is covered by a dielectric cap.
In the fastener disclosed in the above Patent Document, the dielectric cap is positioned on the top surface of the aircraft, so that, in the case of guiding electric shock current of lightning along the top surface of the outer skin, there is a problem that the electric shock current needs to flow around this dielectric cap and the flow of electric shock current is obstructed.
Moreover, from the point of view of Lightning Protection Redundancy required by section 25.981(a)(3) of the FAR (Federal Aviation Regulation) of the United States of America, the abovementioned fastener is not appropriate because of a lack of sufficient countermeasures against deterioration of the dielectric cap due to environmental factors such as ultraviolet rays and damage due to impact from sanddust, lumps of ice and raindrops. Furthermore there is a risk of the dielectric caps peeling off (coming off) from the head section of the fastener during operation of the aircraft.